Power supply rebuild update

Since I got the scope I can finally see what I am doing with the power supply build. After thinking things over for the specs of the power supply I decided to just to go with 30volts and 1.5 amps. Since 90% of most modern electronics you only need 1amp at most so a LM317 with improved ripple rejection is enough to get things working.

Here is a schematic from the LM317 data sheet.


I might try and toss on a current limit/control with either a second LM317 or a differential amp using a LM358 opamp.

For my test build I used a 1n4001 diode and a 10k pot. I didn’t have any 240 ohm resistors so I used a 220ohm and a 12 ohm resistor in series. Works all the same. When I probed the output on a 1k load with the scope it is stable all the way to 30volts. At 30.41 however it goes out of whack. As I said I only need 30 volts.

So far here are the other parts I am using. A transformer that has a max  of 23 volts AC and 35 volts DC and a few secondaries that run from 9 volts AC and 5 volts AC. I pulled it from a old amplifier. Some bridge rectifiers pulled from some old computer power supplies since I am building it as a dual channel I have three rectifiers. Two for the main outputs and a third I plan to use for powering opamps, fan and other misc items. 2200uF caps for smoothing. I have two on each main output and a single 3300uF for the 12volt rail.

For the current limit testing I will try this circuit.


However I would have to change the circuit I am already testing to this.


Might be better in the long run since I will be able to have a option of zero to 30 volts. Also I would add two more POTs to the circuit so I would have a course and fine control for the output voltage. Only issue I will have is the JFETs since I am trying to build this project from what I already have.

I could just keep what I have already put together and toss on the typical current control from the LM317 data sheet.lm317constantcurrent

Or I could copy a diff amp circuit from Dave Jones on the EEVBlog from his uSupply project. There are so many ways to go about this.


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